We determine the curvature of the (pseudo)critical line of QCD with n f =2+1 staggered fermions at nonzero temperature and quark density, by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration, suitably modified to include a nonzero imaginary baryon chemical potential. We work on a line of constant physics, as determined in Ref.[1], adjusting the couplings so as to keep the strange quark mass ms fixed at its physical value, with a light to strange mass ratio m l /ms = 1/20. In the present investigation we set the chemical potential at the same value for the three quark species, µ l = µs ≡ µ. We explore lattices of different spatial extensions, 16 3 × 6 and 24 3 × 6, to check for finite size effects, and present results on a 32 3 × 8 lattice, to check for finite cut-off effects. We discuss our results for the curvature κ of the critical line at µ = 0, which indicate κ = 0.018(4), and compare them with previous lattice determinations by alternative methods and with experimental determinations of the freeze-out curve.

We investigate the dual superconductivity hypothesis in pure SU(2) lattice gauge theory. We focus on the dual Meissner effect by analyzing the distribution of the color fields due to a static quark-antiquark pair. We find evidence of the dual Meissner effect both in the maximally Abelian gauge and without gauge fixing. We measure the London penetration length. Our results suggest that the London penetration length is a physical gauge-invariant quantity. We put out a simple relation between the penetration length and the square root of the string tension. We find that our extimation is quite close to the extrapolated continuum limit available in the literature. A remarkable consequence of our study is that an effective Abelian theory can account for the long range properties of the SU(2) confining vacuum.hep-lat/9504008 * Electronic address: cea@bari.infn.it † Electronic address: cosmai@bari.infn.it

We perform a numerical study of the systematic effects involved in the determination of the critical line at real baryonic chemical potential by analytic continuation from results obtained at imaginary chemical potentials. We present results obtained in theories free of the sign problem, such as two-color QCD with finite baryonic density and three-color QCD with finite isospin chemical potential, and comment on general features which could be relevant also to the continuation of the critical line in real QCD at finite baryonic density

The transverse profile of the chromoelectric flux tubes in SU(2) and SU(3) pure gauge theories is analyzed by a simple variational ansatz using a strict analogy with ordinary superconductivity. Our method allows to extract the penetration length and the coherence length of the flux tube.Comment: 10 pages, 16 figures, 2 tables; accepted for publication in Physical Review

The method of analytic continuation from imaginary to real chemical potential is one of the most powerful tools to circumvent the sign problem in lattice QCD. Here we test this method in a theory, two-color QCD, which is free from the sign problem. We find that the method gives reliable results, within appropriate ranges of the chemical potential, and that a considerable improvement can be achieved if suitable functions are used to interpolate data with imaginary chemical potential.